“...eventually...”
There’s the problem. Eventually probably doesn’t mean next Tuesday. It probably doesn’t mean next year either. It may mean 600 or more years. I think the Crusades ended the last Caliphate in 1400 or so but the Moors came over and started conquering Europe in the late 700’s, I believe. That’s 600 to 700 years of subjugation by Moors.
I suspect things move a lot faster these days. We're already seeing mass sectarian conflicts between the Sunnis, Shiites, Hanafis, Wahabists, al-Qaida types, ISIL, etc.. The only people Iranians hate more than Americans are Iraqis, because they're from a different sect. The more "moderate" muslime states -- Lebanon, Jordan, Egypt, Turkey -- are being torn apart by the extremists in their cultures. It won't take forever for them to realize that either they crush the savages or they will become their victims.
Granted, it won't happen overnight, but I'd say that within the next century, islime will end up a footnote in history.